/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/ShapeFunctions.h
Get the position of the center of a face of the Box. Faces are indexed from 0 to 5, using an ordering where 0/1 are the MinZ/MaxZ faces, 2/3 are MinY/MaxY, and 4/5 are MinX/MaxX
static FVector GetBoxFaceCenter ( FBox Box, int FaceIndex, FVector & FaceNormal )